1. Field of the Invention
This invention relates generally to a redundancy reduction system for a facsimile transmitter-receiver or similar device which uses the scanning beam or element of the transmitter, in its passes across a source document, to detect and store in memory the position of boundaries between data areas of the document and major data-free areas, this stored information being used by the redundancy reduction system to order very fast search of the proposed data-free areas, with accompanying suppression during such search operations of video data transmission to the remote facsimile receiver. This accomplishes a very high order of redundancy reduction by effectively rapidly passing over and skipping transmission of major data free areas, with a resultant reduction of time of use of expensive transmission path facilities.
The present application is related to a co-pending patent application by one of the present inventors, entitled METHODS AND APPARATUS FOR AUTOMATIC BACKGROUND AND CONTRAST CONTROL, now U.S. Pat. No. 3,952,144, Ser. No. 511,422 filed Oct. 2, 1974 by Carl R. Kolker, and assigned to the assignee of the present application. The present application is also related to an issued U.S. Pat. No. 3,843,839 issued Oct. 22, 1974 by Campbell, et al., and also assigned to the assignee of the present application. Both the related Campbell, et al., patent and the related Kolker patent application describe an exemplary facsimile transmission and receiving system in which a source document, whose contents are to be transmitted from a facsimile transmitter to a remote facsimile receiver and reproducer, is scanned line by line, by a narrowly focused light beam which illuminates the document areas being scanned. The light reflected from the scanned document areas is collected by a suitable photo-sensor which is positioned adjacent to the document to produce a corresponding signal which is representative of the shade of darkness or lightness of the document area being scanned at that instant. This video signal is then applied as one input signal to a suitable transmit modulator, which also receives a variety of synchronizing pulses provided by other elements of the facsimile transmitter and operates to transmit both the video information and the synchronizing signal information by a suitable modulation system (as for example by frequency modulation or PCM, etc.) over a transmission path, such as telephone lines or a radio transmission path, to the remote facsimile receiver. The signals which are received over the transmission path by the facsimile receiver, are first processed in a suitable demodulator which extracts both the video portion of the signal and also the synchronizing pulse portions of the signal, and produces a corresponding video input signal and synchronizing pulse signals for use by the receiver. The demodulated video signal is applied as an input to writing means in the facsimile receiver and is applied, for example, to control the intensity of a light beam produced by a flying spot recorder which writes upon a photosensitive recording medium to reproduce thereon the image being scanned by the reading light beam of the facsimile transmitter. The synchronizing pulses extracted by the demodulator of the receiver are applied to the writing apparatus of the receiver to control the positioning of the writing means and are applied, for example, to the vertical and horizontal deflection controls of the receiver to synchronize the horizontal and vertical scans of the writing beam of the receiver so as to illuminate at any time recording areas corresponding to the source document areas then being scanned in the transmitter.
A facsimile transceiver system as described above is disclosed in the Campbell, et al., Pat. No. 3,843,839. An additional module, an Automatic Background and Contrast Control Unit, which may be used with the facsimile system, is disclosed in detail in the co-pending Kolker U.S. Pat. No. 3,952,144. The Automatic Background and Contrast Control Unit corrects the video signal produced by the photosensor for undesired biases, drifts and voltage offsets arising from a variety of sources, and also normalizes the video signal so that it accurately and uniformly represents the full black to white contrast range of the document. The Automatic Background and Contrast Control Unit obtains the information which it needs for such normalizing operations from preliminary calibration scans in which the transmitter automatically makes two scans of a half black-half white calibration strip which is provided on the transmitter target face above the normal source document area. After the initial calibration scans are completed, the Automatic Background and Contrast Control Unit issues a special ADVANCE signal to the vertical deflection unit of the transmitter which has the effect of deflecting the scanning beam down from the calibration strip into the source document area to thereby begin normal line-by-line scanning operations of the areas of the source document. As described in the co-pending Kolker application and in the issued Campbell, et al., patent, such scanning operations of the source document are normally conducted in a uniform and sequential manner, the transmitter making a line-by-line scan at constant horizontal deflection speed across the whole face of the source document and the receiver slavishly following and duplicating these same line-by-line scans on the recording surface on which the source document is to be reproduced in the receiver.
Such uniform transmission on a line-by-line basis of all areas of the source document is relatively slow for the reason that the maximum useable horizontal deflection speed of the transmitter scanning beam is limited by the band width capability of the transmission path utilized between the transmitter and the receiver. This is especially true with narrow band transmission paths such as phone lines and to a certain extent, conventional commercial radio channels. Transmission time over commercial transmission paths is very expensive and as a result, the relatively slow speed of transmission of a facsimile system of the type described is directly reflected in a corresponding relatively high cost of message transmission.
The present application is concerned with another system (and corresponding module) which may be used with the bacis facsimile transmit-receiver system. The added module is called a Redundancy Reduction Unit and provides a very major speed-up of transmission time by using information available in the transmitter to sense and locate boundaries between data filled areas of the document and probable major data free areas of the document and in accordance with such sensing to provide the transmitter with a number of fast search modes in which the transmitter very rapidly sweeps its scanning bean in a search pass across proposed data free areas while simultaneously suppressing all transmission of corresponding video data to the receiver during such fast search modes. Fast search in a horizontal direction is effected by increasing the speed of horizontal deflection of the scanning beam in a major data free area. Fast search in the vertical direction is effected by two related methods, these being: first, the use of a wide search pass in which the scanning beam is effectively widened during a horizontal pass, preferably by zigzagging the beam up and down with a simple vertical modulation which is many lines wide; and secondly, by thereafter making an increase in the size of the incremental vertical advance or vertical deflection between successive wide search passes of the scanning beam so that each wide search pass is overlapped with the bottom of the preceding wide search pass.
The overall result of these procedures is that major data free areas in a horizontal direction are scanned at a much higher velocity than normal and major data free areas in a vertical direction are scanned with many fewer passes of the wide search scanning beam. In a preferred embodiment this increased speed is obtained with no additional burdening of the information handling capacities of the transmission path or receiver. With a conventionally type-written letter as a source document, transmission time over a normal telephone line is reduced from an average of approximately 6 minutes to an average of approximately 1 minute.